Pressure and flow events during late systole will be used for identifying features of the left ventricle (LV), and systemic arteries (SA) that participate importantly in LV/SA interaction. The relevant LV and SA properties needed to explain interaction during the late systole have not been previously described. Relevant LV properties give rise to separable fast and slow processes. The relationship between these fast and slow processes are considered responsible for creating "positive" and 'negative' effects during late systole where positive and negative effects are defined by referencing the pressure of an ejecting beat to the pressure of an isovolumic beat at an equivalent volume and time. Specific hypotheses, based on a prototype mathematical representation of underlying kinetic processes, are advanced and experiments in the isolated ferret heart are proposed to test these hypotheses. Fast responses are separated from slow responses and are tested individually. Additionally, experiments are proposed to evaluate the mechanistic basis of fast and slow responses. Results of experiments will lead to modification of the prototype model such that an adequate representation of LV dynamics will emerge. Relevant SA properties give rise to wave reflections from two effective sites at the termination of two effective wave transmission paths, one directed headward and the other directed to the posterior portions of the body. Experiments in the open-chest ferret are designed to evaluate the physiological variation in these properties and their resultant behavioral effects under physiological and pharmacological interventions. Interaction occurs when extra effort is needed by the LV to deliver outflow against reflected waves arriving during late systole. LV properties responsible for positive effects are needed to maintain ejection during these late systolic periods. It is argued that sustained ejection during late systole is energetically advantageous. Eventually, LV properties responsible for negative effects override those responsible for positive effects to bring about a rapid relaxation and time for adequate filling. Experiments to test this interaction hypothesis are proposed using an isolated ferret heart and a simulated arterial system where the simulation is an asymmetric T-tube wave-transmission model. It is proposed that late systolic LV/SA interaction is sensitive to the physiological state of both the LV and the SA and plays an important role in normal and modified cardiovascular function.